[RT-AC56U] Reboot cycle after update to original firmware 374.291

[RMerlin]

I've been trying like mad 3 hours doing different stuff without luck.

Just to triple check, the procedure would be:

1. Turn off the router
2. Press the WPS button
3. Turn it on
4. Count 10 seconds
5. Press the Reset button releasing the WPS button at the same time
6. Count 5 seconds
7. Release the Reset button

Once I release it (when getting the exact milisecond), it would blink, right?

Thanks in advance... spent a lovely sunday watching at my $200 new brick (after 5 days of use)

Yes, unless the nvram contents data preventing the CFE from even properly processing the WPS or reset button. I've seen it happen with the RT-AC56U.

 

[Alpha7]

Yes, unless the nvram contents data preventing the CFE from even properly processing the WPS or reset button. I've seen it happen with the RT-AC56U.

I am running into the same issue. The router will be on for about 20 seconds than reboot. I tried the WPS for 10-15 then the rest button to no avail. It just sits rebooting every 20 seconds.

If the WPS option fails what is the next step to try to salvage this thing?

 

[RMerlin]

I am running into the same issue. The router will be on for about 20 seconds than reboot. I tried the WPS for 10-15 then the rest button to no avail. It just sits rebooting every 20 seconds.

If the WPS option fails what is the next step to try to salvage this thing?

Either a serial cable, or to be lucky enough to hit some window during which one of the two buttons will work.

 

[-KS-Silence[AU]]

For those who can get the router to the state of a flashing power LED, Atleast on a RT-AC66U anyway, you should then be able connect a lan cable to the router and a computer with nothing else connected and bring up the CFE Loader in a broswer skipping the need for the Firmware tool.

This MAY NOT work for you, but it will for some, and the bonus is you dont need a Windows based computer if it does MAC / Linux / Unix with a web broswer will do, even a tablet with ethernet.

Couple of Merlin FW Builds ago my router used to randomly and freqently fail to boot when power cycled (you could sometimes cycle it many times without issue) and usually would sit in recovery though sometimes i had to prod it....

From a flashing Power LED the process if it works is rather straight forward.
For this Assume the router was configured with an IP of 192.168.2.1 (you need to adjust your IP's to suit how your device was configured)
Prerequisites:
1x Ethernet cable
1x Computer / tablet with ethernet and web broswer
1x Known good Firmware file for the model of router in trouble
and a bit of patience

1. Connect a ethernet cable between a computer and LAN1 on the router, Make sure no other network cables are connected.
2. Set a static IPv4 address on the computer, preferably 192.168.2.2 in this scenario
3. Open a web broswer and enter the routers IP, the CFE recovery page should load. If it does you should be fixed within 5 Minutes.
4. if the problem was caused by bad configuration --> Click on Set Defaults / Clear NVram (cant exactly remember the exact name of it, but its obvious if you look ).
5. If the problem was a bad firmware flashing --> Make sure you have a Known good firmware file handy, From the CFE page Select and upload this to the router and let it flash.
6. If instructed to --> Turn OFF the router for atleast 30 seconds then turn it back on
7. Hopefully..... $ PROFIT!

In some cases you will need to BOTH Default the Device AND Reflash it.

In my case it didnt appear to be bad configuration that caused my router to enter recovery, all i had to do was reflash from CFE, i did not have to reset the settings or anything, and after reflashing it would load it configuration and be happy days.

Hopefully this is of some use to others, especially those without the Firmware Restoration tool handy.

PS. Merlin / Mods, you might want to edit and Sticky this somewhere for others, its a potential Time saver.

 

[Alpha7]

Silence,

Funny thing is when I opened my router out the box (it was an open box) it came up to that CFE recovery page. I cleared NVRAM and got it working screwed it up myself to this point though .

I will likely return it but Merlin has anyone posted the serial pin-out for this router yet? I searched around a lot but couldn't find anything. Trying to save the time of the trail and error + I'm not that experienced with the serial method (lucky have friends that are though)

Either way thanks both of you. Hopefully that CFE and playing with the buttons with help someone else.

 

[RMerlin]

Silence,

Funny thing is when I opened my router out the box (it was an open box) it came up to that CFE recovery page. I cleared NVRAM and got it working screwed it up myself to this point though .

I will likely return it but Merlin has anyone posted the serial pin-out for this router yet? I searched around a lot but couldn't find anything. Trying to save the time of the trail and error + I'm not that experienced with the serial method (lucky have friends that are though)

Either way thanks both of you. Hopefully that CFE and playing with the buttons with help someone else.

Unfortunately I closed my AC56 casing (and this one's a pain to open) so I can't check at the moment. I used a multimeter to determine the correct pinout, so it should be fairly easy. The most important thing is to determine which pin is the ground (easy to find if you check for a resistance of 0 between a pin and any ground point on the router). The next two pins will be tx and rx (forgot which order). The last pin will be VCC - you do not want to connect this one.

 

[Destructo78]

Hey guys,
Glad I came across this forum! I've read through the thread and was wondering if any of the following sounds familiar. Briefly, I flashed December's firmware release from a previous version of Merlin and you guessed it....boot looping nightmare!
So, after taking a break from trying to get the device into rescue via the WPS and Reset buttons, etc.. I connected it directly to my network card and had some seemingly weird results.
I can ping 192.168.1.1 with success but it's also showing the host is unreachable??
I can open up my web browser and go to http://192.168.1.1, https://192.168.1.1, and xxxxx.asuscomm.com:8443 but only to see the 'device is restarting, enter the new IP and/or port to connect......'
(sorry, don't have that screen right in front of me but it's the same page that loads after changing a setting while the router boots back up)
All of this aside, any portscan of the same IP shows a dead host.
Lastly, my network status shows that is connected to an 'unidentified network' with no network access...that is until it reboots a few seconds later and shows a cable is disconnected. However, the uptime of the connection will continue to increase. WTF! LOL
Sorry for the long description, but I AM STUCK!! I will be pressing and releasing various button combinations and the like until I hear from you guys!!! ;/

 

[gervasio]

Good luck with that... I gave up after 3 days of trying every combination

 

[RMerlin]

I just had to recover my own AC56U from badly corrupted nvram, where neither buttons would work, and the router would also be unable to configure its own network interfaces (so no web interface to recover it). The corrupted nvram even prevented the kernel from loading, so no serial console either.

After a lot of tinkering, I finally managed to access the CFE over serial. The trick (using a serial cable) isn't to repeatedly mash Ctrl-C like I usually do, but to keep Ctrl-C constantly pressed as you turn the router on. Looks like the opportunity window is *very* small. It will abort the boot process and land you in CFE, where you can do an "nvram erase" over serial, followed by "reboot". Next reboot, you should now be able to access Recovery Mode as usual, through the Reset button.

So if anyone has an apparently bricked RT-AC56U, you can almost certainly recover it using a TTL serial cable.

As for the pinout, now that I have it open in front of me...

+-+
|1| VCC (do not connect)
|2| TX
|3| RX
|4| Ground
+-+

This is with the Ethernet ports closest to you. Pin 1 of the serial port has a white stripe on the pcboard by that pin. You have to connect Tx, Rx and Gnd.

Remember that you need a TTL adapter. You cannot directly connect it to a serial port. Those adapters are about 5-7$ on eBay if I remember. And since Asus is even providing pins on the router's pcboard, you won't have to do any soldering at all.

 

[mobileman88]

I just had to recover my own AC56U from badly corrupted nvram, where neither buttons would work, and the router would also be unable to configure its own network interfaces (so no web interface to recover it). The corrupted nvram even prevented the kernel from loading, so no serial console either.

After a lot of tinkering, I finally managed to access the CFE over serial. The trick (using a serial cable) isn't to repeatedly mash Ctrl-C like I usually do, but to keep Ctrl-C constantly pressed as you turn the router on. Looks like the opportunity window is *very* small. It will abort the boot process and land you in CFE, where you can do an "nvram erase" over serial, followed by "reboot". Next reboot, you should now be able to access Recovery Mode as usual, through the Reset button.

So if anyone has an apparently bricked RT-AC56U, you can almost certainly recover it using a TTL serial cable.

As for the pinout, now that I have it open in front of me...

+-+
|1| VCC (do not connect)
|2| TX
|3| RX
|4| Ground
+-+

This is with the Ethernet ports closest to you. Pin 1 of the serial port has a white stripe on the pcboard by that pin. You have to connect Tx, Rx and Gnd.

Remember that you need a TTL adapter. You cannot directly connect it to a serial port. Those adapters are about 5-7$ on eBay if I remember. And since Asus is even providing pins on the router's pcboard, you won't have to do any soldering at all.

What is the exact description of the type adapters? Thanks

 

[RMerlin]

What is the exact description of the type adapters? Thanks

Serial to TTL adapter or USB to TTL adapter.

Here's a list of such devices:

http://www.ebay.com/bhp/usb-to-ttl-serial-cable

The one I have is one of those with a CP2102 interface.

 

[dekozi]

I just bought an Asus RT-AC56U and as soon as i took it out of the box, i updated the firmware to the latest one (Firmware version 3.0.0.4.374.542). I rebooted the router and plugged my USB drive (Seagate GoFlex 3TB) and the router went into a reboot cycle. If i unplug the drive, the router comes back up normally, but keeps on rebooting if the USB drive is plugged in. I returned the router in exchange for another one of the same model. I took the router out of the box and without updating the firmware, i turned on the router and plugged in my USB drive. The router came up, and stayed on like it should. I updated the firmware again to the latest one mentioned before, and the same issue happened again. I tried downgrading the firmware to later versions, boot into recovery mode and clearing NVRAM, restore defaults, and nothing worked. Has anyone experienced this issue?

 

[L&LD]

Yes, read/search the forums. Known issue with some USB drives.

Try a different drive if you can.

Try the RMerlin 374.38_2 firmware too (you may have to use the USB 2.0 port though until RMerlin has finished the xxx.39 build).

 

[Injuis]

Serial to TTL adapter or USB to TTL adapter.

Here's a list of such devices:

http://www.ebay.com/bhp/usb-to-ttl-serial-cable

The one I have is one of those with a CP2102 interface.

Merlin, you help us so much - thank you.

I purchased one of these per Merlin's suggestion and couldn't get it working. It turns out I had to switch the TX and RX for it to communicate through Putty correctly. Ran the command on CFE and now I'm back up! I think our boot-loops are permanently over when using this method. It's just a pain to open this thing up.

For the people totally new to this:
1) Purchase the adapter mentioned above and install the drivers it comes with
2) Connect GND, TX, and RX to router pins, avoiding the pin with the white stripe (I had to flip TX and RX on my adapter)
3) Download PuTTy and configure the serial connection for

COM port: Should match the one assigned by OS
Baud: 115200
Data Bits: 8
Stop Bits: 1
Parity: None
Flow Control: None
​

4) Click 'Open' in PuTTy to begin session
5) Turn on router and immediately hold CTRL-C to prevent normal boot mode
6) If you are succesful you will see "CFE>" in your PuTTy console
7) Type in the command 'nvram erase' and execute
8) FIXED

A note on opening this thing: Make sure to take off that metal foot clamp at the bottom, then the two screws behind the label on the back. The actual shell can just be brute forced off by splitting the housing at the connection points (2 on each of the sides, 3 on top)

 

[dekozi]

Yes, read/search the forums. Known issue with some USB drives.

Try a different drive if you can.

Try the RMerlin 374.38_2 firmware too (you may have to use the USB 2.0 port though until RMerlin has finished the xxx.39 build).

Can you tell me where i can look or what i should search for? I have been looking for days and i can't find more info.

 

[gervasio]

Merlin, you help us so much - thank you.

I purchased one of these per Merlin's suggestion and couldn't get it working. It turns out I had to switch the TX and RX for it to communicate through Putty correctly. Ran the command on CFE and now I'm back up! I think our boot-loops are permanently over when using this method. It's just a pain to open this thing up.

For the people totally new to this:
1) Purchase the adapter mentioned above and install the drivers it comes with
2) Connect GND, TX, and RX to router pins, avoiding the pin with the white stripe (I had to flip TX and RX on my adapter)
3) Download PuTTy and configure the serial connection for

COM port: Should match the one assigned by OS
Baud: 115200
Data Bits: 8
Stop Bits: 1
Parity: None
Flow Control: None
​

4) Click 'Open' in PuTTy to begin session
5) Turn on router and immediately hold CTRL-C to prevent normal boot mode
6) If you are succesful you will see "CFE>" in your PuTTy console
7) Type in the command 'nvram erase' and execute
8) FIXED

A note on opening this thing: Make sure to take off that metal foot clamp at the bottom, then the two screws behind the label on the back. The actual shell can just be brute forced off by splitting the housing at the connection points (2 on each of the sides, 3 on top)

After more than 2 months patiently waiting for the TTL cable to arrive... I FIXED IT!!!!!! THANKS TO YOU BOTH GUYS!!!!!!!!!!!!!!!!!!!!!!!

 

[ninelo]

Cannot get a CFE>

Guys!
I have the same problem after simple update from 40 to 41 beta via WEB GUI.
Pushing reset and wps buttons in any order does not work.
The router cannot boot normally and cannot enter recovery mode, anyway.
What happens? Pushing power on > Power LED shines constantly, WAN and LAN LEDs periodically blink, meaning that the router in boot loop.
The last chance was to try using UBS TTL adaptor and CFE mode.
What I've got?
A USB 2.0 UART TTL CH340G. This is it http://www.squirrel-labs.co.uk/usb-to-ttl-uart-6pin-ch340g-module.html
Connected to the router pins as described, checked pins with a multimeter, found a ground and the next were RX and TX.
PC Win7 Win8 Win XP, tried on all of them.
Drivers installed successfully, com port assigned.
Running Putty, configuring as described above, starting session. As I don't see any error messages I guess session is started. Just a black terminal window.
Powering on a router and immediately holding Ctrl+C. Moreover I tried holding Ctrl+C before powering on.
No luck. A router switches on, WAN and LAN LEDS start lighting constantly, a putty terminal windows stays blank.
A few questions
1. What I am doing wrong?
2. How long should I hold Ctrl+C? Just seconds, minutes, hours?
3. Is it a correct behavior of WAN and LAN LEDs when I power on the router connected to the serial port?
4. What else can I do to save my router?

Thanks in advance.

Upd. Completely read this guide http://dd-wrt.com/wiki/index.php/Serial_Recovery, very useful. Checked in troubleshooting whether the adaptor works. Connected RX and TX together, opened a terminal session and typed on the keyboard to see if my typed characters are echo'd correctly in the terminal. Could see what I typed. So the adaptor is working.

UPD2.
Hooray! Hooray! Hooray!
I have recovered my router!
BUT! A little bit another way. It should be added to FAQ.
The only tip was to change the order:
1. I took the router NOT connected to the Serial.
2. Switched it ON. It started its bootloop.
3. Then I connected the router to the Serial. And I saw the log in terminal. First luck.
4. After that I started constantly hold CTRL+C and in one moment ... I saw the desired CFE>!
5. Then erased nvram - router booted normally. Congrats!

 

[Winux2]

Sadly, the RT-AC56U bootloader is seriously bugged. In some situations, it will have trouble dealings with some stored nvram values that will make it fail to handle the reset and WPS buttons, in addition to failing to configure the network interface. The only solution I found in these cases was to hook up a serial cable, and use it with the firmware's initial console that gets initialized later during the boot stage to be able to erase the nvram content.

That was one of the reasons why I advised against playing with overclocking on the RT-AC56U. I suspect that some firmware versions might also lead to that same situation.

I suspect that might be what's happening to you. You already had nvram settings that prevented the bootloader from working properly, and you flashed a firmware that fails to properly boot, leading you to being stuck in a boot loop. If that's the case, the only solution I could find is opening the router and using a serial cable.

My 2 week-old (May 2014) RT-AC56U router (FW:RT-AC56U_3.0.0.4_374.42_2) is now a brick after attaching a second USB drive (160GB Fat32) to the USB2 port. A 2-TB ntfs USB drive was attached to the USB3 port.

After attaching a 2nd drive, the Routers Web GUI was only partially visible (bottom half) the top half was missing and none of the visible links functioned.

I turned the router off, then back on, and entered the Web GUI, which remained the same in 3 web browsers (IE11, Chrome & Firefox). I pressed the routers reset button in hopes it would resolve the issue. Now the router fails to boot, and only the Power Led lights up (steady, not flashing). I've tried most the Resetting suggestions (except the serial connection) to revive the router, to no avail.

I like the features of this router. However, if this routers boot loader and nvram are problematic, maybe I should buy another model or brand.

Is the RT-AC56U router worth the hassle of fixing, repairing, or replacing?
Any thoughts or ideas of what might have caused the firmware corruption?

 

[RMerlin]

My 2 week-old (May 2014) RT-AC56U router (FW:RT-AC56U_3.0.0.4_374.42_2) is now a brick after attaching a second USB drive (160GB Fat32) to the USB2 port. A 2-TB ntfs USB drive was attached to the USB3 port.

After attaching a 2nd drive, the Routers Web GUI was only partially visible (bottom half) the top half was missing and none of the visible links functioned.

I turned the router off, then back on, and entered the Web GUI, which remained the same in 3 web browsers (IE11, Chrome & Firefox). I pressed the routers reset button in hopes it would resolve the issue. Now the router fails to boot, and only the Power Led lights up (steady, not flashing). I've tried most the Resetting suggestions (except the serial connection) to revive the router, to no avail.

I like the features of this router. However, if this routers boot loader and nvram are problematic, maybe I should buy another model or brand.

Is the RT-AC56U router worth the hassle of fixing, repairing, or replacing?
Any thoughts or ideas of what might have caused the firmware corruption?

The original symptoms you describe are more related to either a disk label containing illegal characters, or a device on your network using an invalid hostname. This will lead to the webui failing to completely load due to a Javascript error, it's rarely related to nvram content.

Make sure you do unplug your USB disks while troubleshooting the router. Also ideally, only plug one single computer to it for the recovery process.

Have you tried the factory default reset using the WPS button at power up?

 

[Winux2]

The original symptoms you describe are more related to either a disk label containing illegal characters, or a device on your network using an invalid hostname. This will lead to the webui failing to completely load due to a Javascript error, it's rarely related to nvram content.

Make sure you do unplug your USB disks while troubleshooting the router. Also ideally, only plug one single computer to it for the recovery process.

Have you tried the factory default reset using the WPS button at power up?

The disk labeling seems normal, one is WD Ultra 2TB and the other is WinUx2. However, now that I checked the labels, at the time I plugged in the WinUx2 USB drive, I didn't realize it was named similar to the the hostname which was winux2 (all lower case). Perhaps that caused the javascript error?

The 1st time I pressed the Factory default reset, both drives were attached, along with the wan and lan connections, and the router failed to fully reboot, only the power led came on (steady, not flashing).

The 2nd+ times, I removed all devices from the router and the Factory default reset fails to work. The router is in an endless reboot state and will not go into recovery mode, even after pressing WPS button at power up.